NOPE, your all wrong, sorry. no o'ring, no part number, just when out side, too the tarp off my mk3, and pulled the dipstick, NO O'Ring at all, 366K miles with out one and not so much as a drop out of that part or it not seating securely, its quite stiff fitment and i see no reason to add one. Replace the dipstick cap and the dipstick if its leaking as they do get brittle from age.
Again, no it does not, for the AHU and the ALH both use the same part number.
/thread